Technology and technics of ore preparation processes
9
Many operating processing plants face challenges that were absent at the early stages of their activity. Processing involves ore minerals extracted from new deposits or ore tak-en at deeper levels in the existing mines. In this case, not on-ly content of useful components but also physico-properties (hardness, abrasiveness) of ore can change. These factors, as a rule, add value of the final marketable concentrate. Un-der the circumstance, many operating processing plants search for ways of increasing the production output.
One of the promising directions toward this problem handling is modernization of ore pretreatment charts using high pressure grinding rolls (HPGR) as an additional stage of fine crushing of before milling. Reduction of crushed ore size enhances output of milling equipment by 15–20% (some-times even higher) depending on characteristics of ore and on the current ore pretreatment chart [1].
Since first introduction of HPGR in cement production in 1986 for clinker grinding, designers have made progress in update of the mill structure and selection of materials re-quired to make rolls, which has resulted in the increased ef-ficiency of HPGR up to 94%; furthermore, maintainability and serviceability of the mills has grown [2, 3].
Modern HPGR have very small dimension and, this, need smaller understructure as against conventional cone crushers. HPGR have low vibration and noise level, and ore dust in the course of breakage is readily removed by aspira-tion systems.
At present HPGR are produced by many machine-buil-ding companies. The key position belongs to Polysius (Thys-senKrupp Resource Technologies GmbH), KHD (KHD Hum-boldt Wedag AG) and Köppern (Maschinenfabrik Köppern GmbH & Co KG), which are Germany companies. All manu-facturers adhere to the same layout diagram of the mill as shown in Fig. 1, with different designs of individual units.
UDC 622.732
N. O. TIKHONOV (JV “IVS”)
A. N. IVANOV (RIVS Science and Production Association)
ORE PRETREATMENT REENGINEERING AT OPERATING
PROCESSING PLANTS USING HIGH PRESSURE
GRINDING ROLLS—A PROMISING AREA OF ACTIVITY
(IN TERMS OF ERDENET MINING CORPORATION)
A. N. IVANOV, Director of Department
N. O. TIKHONOV, Head of Subdivision
Ore pretreatment is the most money-taking stage of mine-ral processing at a plant. For this reason, enhancement of ore pre-
treatment processes is one of the allocated targets of the produc-tion improvement in mineral dressing industry.
Reengineering of ore pretreatment charts using high pressure grinding rolls (HPGR) as an additional stage of fine crushing of ore before feeding to milling cycle is a promising area of activity, which sometimes enables enhanced ore pretreatment efficiency at operating processing plants. Owing to reduced grain size of ore feed for milling, the milling equipment capacity grows by 15–20% depending on characteristics of an ore type and on the current ore pretreatment chart.
It is indispensably required to assess expediency of HPGR tech-nology by means of laboratory and pilot-plant testing aimed at characterization of the behavior of ore in work zone of HPGR.
The current performance of the available crushing and grind-ing equipment and its test data provide source information for the JKSimMet simulation applied by RIVS to construction of mathe-matical model enabling high-reliable prediction of the production data obtained using an ore pretreatment chart depending on changes in the chart and in the equipment parameters.
The authors illustrate prospects of the described approach in terms of the technical-and-economic calculation project “Reengi-neering of ore pretreatment phase I, crushing stage IV” accom-plished by RIVS for the processing plant of Erdenet Mining Corpo-ration.
Improvement of ore pretreatment processes has always been a priority trend mining and processing modernization since ore pre-processing is the most expensive process stage of beneficiation.
One of the promising directions, which in some instances has enabled effectivization of ore pre-processing at operating plants, is redesign of an ore pre-processing circuit by introduction of high pressure grinding rolls as an auxiliary stage of fine crushing of ore before grinding. Reduction of size of the ore grinding feed allows the increase in the milling equipment output by 15–20% depen-ding on features of a specific ore type and on characteristics of the current ore pre-processing chart.
In order to estimate material behavior in the work zone of HP-GR, laboratory and semi-commercial tests are carried out as a compulsory stage of feasibility study of the technology application under certain conditions.
At the present time, RIVS is designing new charts and up-grades the existing schemes of ore pre-processing based on the test data and current process indexes of crushing and grinding equip-ment on hand using JKSim computer simulation software pack-age. The obtained mathematical model allows high-reliable fore-casting of the production data of the ore pre-processing chart at varied parameters of the involved equipment.
As an illustration of the described approach, the article pre-sents the technical-and-economic calculation for “Ore Pre-Proces-sing Stage I Technical Upgrading, Crushing Stage IV” accom-plished for the processing plant of Erdenet Mining Corporation.
plates, other components; � Body frame; � Lubricating system. The prime objective of planning ore pretreatment with
HPGR is the selection of the machine dimension to ensure the desired capacity of the preset reduction in crushed ore size. Capacity of HPGR is mainly governed by the geometry of rolls, type of lining shells and physico-mechanical proper-ties of ore mineral to be ground. For the chosen dimension HPGR, its capacity is adjusted by means of the roll speed.
The grain-size composition of the mill product is con-trolled by grinding force between rolls, owing to which the mill product undergoes high pressure in the compression zone, which, in its turn, results in micro-fracturing and break-age of minerals. At the present time, the grinding force and grain-size composition are correlated experimentally for each material type in the course of testing.
After preliminary laboratory research and semi-com-mercial trials, the next indispensable stage is estimation of HPGR expediency in the particular application conditions. The estimation involves:
� General consistency of the test ore and high pressure grinding method;
� Key process parameters of HPGR (unit capacity, unit compression force and unit energy input);
� Grain-size composition of ground material; � Abrasing effect of ore on lining shell walls. The analysis record includes some parameters, for in-
stance, the true and bulk specific gravity of ore, pre-break-
age grain-size composition, moisture content, bulk gravity of ore after compression in work zone of rolls, speed of rolls, to-tal grinding force, wattage used, pressure of pressurization system, spacing of rolls before feeding the mill, spacing of rolls in work; specific energy consumption, capacity, grain-size composition of ground product (sampled in the middle and edge zones, and of total discharge), ratio of products from the middle and edge zones.
Based on the test data and the current production data of the available crushing and grinding equipment, using JK SimMet simulation computer software package applied by RIVS to development and modernization of ore pretreatment charts, the mathematical model has been constructed for highly reliable forecasting of production data of an ore pre-treatment chart depending on the change in the milling and equipment parameters.
By way of illustration, the data of the process design im-plemented by RIVS within the framework of the project on “Reengineering of ore pretreatment phase I, crushing stage IV” at the processing plant of Erdenet Mining Corpora-tion. The process design was aimed at development of an ore pretreatment technology to increase ore crushing and trans-portation capacity from actual 20.6 Mt/yr up to 25 Mt/yr with-out additional milling equipment.
With the intent to prove applicability of HPGR in the co-operating conditions of Erdenet Mining Corporation, refine-ment of estimated production data and selection of the mill work mode, the process of ore breakage by high pressure rolls was tested on a pilot stand of the Thyssen Krupp labora-tory for the purpose of determining:
� Grinding force required;� Effect of moisture content of the feed on the properties
of the ground material, and on the output and wear of the mill; � Specific capacity; � Circulating load; � Adjustment of Bond Ball Mill Index of HPGM product. Based on the test results and subsequent calculation da-
ta, it is concluded that HPGR will allow reduction of ground ore size with the simultaneous increase of 2.5 mm size grade in the ground ore content up to 50–55%. That will enable higher capacity of the same milling equipment and the required size of the ground product for further dressing stages.
Erdenet Mining Corporation uses the classical three-stage crushing chart with the closed cycle at stage III (fine crushing) for ore pretreatment. The flow chart (including mill-ing stage I) is shown in Fig. 2.
Dump trucks bring ore –1000 mm in size from open pit mine to two crushers KKD-1200/130GRSHCH. In front of the crushers, there are bar screens with a slot width of 150 mm. Oversize product goes to the crushers, and undersize is mixed with the crushed ore –250 mm in size and fed to hop-pers, wherefrom feeders and belt conveyors carry it to a coarse-crushing ore storehouse.
Crushing stage II (open cycle with screens GPKT-72U) uses crushers KSD-2200T2-D (5 crushers). The crushed product is transported to an intermediate storage facility in the mid- and fine-crushing area. Then, the ore is milled by fine crushers KMD-3000T2-DP (6 crushers). The oversize product of screens GPKT-72U installed ahead of the crush-ers is returned to the mid-crushed ore storage facility, which forms the closed cycle of fine crushing.
Fig. 1. HPGR: general view and structural components
EURASIAN MINING • 1. 2015
Technology and technics of ore preparation processes
11
The undersize product of all medium and fine crushing screens (rated size d95 = 14.8 mm) is conveyed to a fine-crushing ore storehouse, wherefrom it is fed to milling stage I (6 mills MSHCHTS-5500×6500 and 3 mills MSHTS- 5800×6900); the mills operate in a closed cycle with three-product cyclone GTS-1400. Fine discharge of the cyclones, with 65% content of –0.074 mm size grade, flows by gravity to a conditioning tank for treatment prior to bulk flotation.
Efficiency of the entire process is governed by the per-formance of the closed cycle of the fine crushing stage. The available crushers, given the current size grade of the feed, are incapable of increasing the processing capacity more than by 5–7% with keeping the required size of the ground ore.
It is worthy of mentioning that Erdenet company has done its best in upgrading and reequipment of ore pretreat-ment, which enabled enhancement of processing capacity from the design value of 16 Mt/yr up to the actual level of 20.6 Mt/yr. The goal was achieved owing to replacement of fine crushers KMD-2200 for crushers KMD-3000T2-DP, in-clusion of additional crusher KMD-3000T2-DP in the medi-um- and fine-crushing circuit, and replacement of the avail-able screens for the more efficient models. That resulted in the reduction of the ground product size from 25 to 14.8 mm, which ensured enhanced capacity of the process with the available milling equipment.
However, all reserves are now depleted and further in-crease in the processing capacity is impossible without a drastic change of the ore pretreatment technology. At the same time, RIVS and Erdenet have carried out full-scale reequipment of flotation area, which offers an opportunity of expanding essentially the processing capacity.
In accord with the developed engineering designs, it is suggested to operate fine crushers in open cycle mode, which will eliminate cycling loading of the crushers and ena-ble higher processing capacity without additional crushers at fine crushing stage III, while the fine crushing product will be sent to milling by HPGR operating in a semi-open cycle with recirculation of middlings having the highest content of larg-er-size fractions. The flow chart with the use of HPGR (in-cluding milling stage I) is shown in Fig. 3.
In conformity with the engineering decisions, the milling feed size (d95 — grain size by 5% screenings; dw.a — weight-ed average grain size; F80 — grain size by 20% screenings) will change as follows:
� currently (after crushing by KMD): d95 = 14.8 mm, dw.a = 7.5 mm, F80 = 12.2 mm;
� project (after milling by HPGR): d95 = 10.8 mm, dw.a = = 2.9 mm, F80 = 7.1 mm.
Furthermore, as follows from the test results, HPGR al-low reduction in the Bond Index by 10% due to weakening of ore under high pressure [1]. Owing to this, the enhancement
Fig. 2. Current production process ore pretreatment
phase I at processing plant of Erdenet Mining
Corporation (annual processing capacity 20.6 Mt)
Initial ore,–1000 mm2687.9 t/h
Bar screen
–250 mm,806.4 t/h
+250 mm,1881.5 t/h
Coarse crushing,KKD 1200/130GRSHCH, 2 crushers
Hopperd95–250 mm
d95–70 mm
Feeding,4 feeders
Coarse-crushing ore storage
Feeder –250 mm,3077.9 t/h
Medium crushingKSD-2200T, 5 crushers
ScreeningGPKT-72U,5 screens
–70+14 mm,1734.1 t/h
–14 mm,3077.9 t/h
Medium-crushingore storage
Fine-crushing ore storage
Feeding,6 feeders –70+14 mm,
2620.2 t/h
Feeder,8 feeders 65% content of grain
size –0.074 mm, 2028 t/h
–14 mm,2551 t/h
To flotation65% content of grain size –0.074 mm2147.9 t/h
–14 mm,1108 t/h
45% content of grain size –0.074 mm,523 t/h
65% content of grain size –0.074 mm,119.9 t/h
Fine crushing,KMD-3000T2-DP,6 crushers
–14 mm,1969.8 t/h
–25+14 mm886.1 t/h
9999.9 t/h
9999.9 t/hClassification,GTS-1400
8% content of grain size –0.074 mm,7448.9 t/h
Classification,GTS-500
Milling stage I, 9 mills 22% content of grain size –0.074 mm,403.1 t/h
Milling stage II
ScreeningGPKT-72U,6 screens
Technology and technics of ore preparation processes
12 EURASIAN MINING • 1. 2015
of the ore processing capacity by 20% and maintenance of the designed capacity of 25 Mt/yr is achievable with the available milling equipment.
The scope of work performed by RIVS included also de-sign solutions on arrangement and structure of milling equip-ment.
According to the economical estimate, the payback time of the new equipment will take 2 years and 9 months starting from the commissioning period.
Mills HPGR are surely not a broad-based solution. In each particular case, it is required to analyze the current con-ditions and characteristics of a particular ore material, to car-ry out trial test and, then, computer-aided modeling of the performance prediction ended with a detailed economical design.
However, it is indubitable that HPGR creates favorable conditions for next following production processes. Potential saving of energy for further grinding (and the entire ore pre-treatment cycle) results in appreciable cut-down of capital and operating costs. The introduction of HPGR makes feasi-ble processing of low-grade ore, which is impossible with the conventional technologies of crushing and semiautogenous milling.
RIVS Science and Production Association maintains working partnership with leading HPGR manufacturers, is in possession of ample experience in ore pretreatment design
and modernization, and holds advanced computer-aided en-gineering tools (program JKSimMet and proprietary soft-ware). Design office RIVS-Proekt, being the part of RIVS, practices innovative design solutions, thus, allowing RIVS to accomplish the required scope of work connected with fruit-ful commissioning of HPGR, starting from arrangement and execution of the required research and economical analysis of the new machinery expediency and closing up with engi-neering documentation delivery and technical support of the project actualization on site.
References1. Morsky P., Klemetti M., Knuutinen T. A comparison of
high pressure roller mill and conventional grinding. Procee-dings of XIX International Mineral Processing Congress. 1995. Vol. 1. pp. 55–58. SME.
2. Klymowsky R., Cordes H. The Modern Roller Press — Practical Applications in the Ore and Minerals Industry. Auf-bereitungs Technik. 1999. Vol. 40, Nо. 8. pp. 387–396.
3. Putzelt N., Knecht J., Burchardt E., Klymowsky R. Chal-lenges for High Pressure Grinding in the New Millenium. Seventh Mill Operators Conference. Kalgoorlie, 2000. WA. pp. 47–55.
Tikhonov Nikolai Olegovich, Ivanov Alexander Nikolaevich,
